Thursday, June 27, 2013

[Herpetology / Evolution • 2009] A Central Role for Venom in Predation by Varanus komodoensis (Komodo Dragon) and the Extinct Giant Varanus (Megalania) priscus

Fig. 2. Anatomical investigation of the Varanus komodoensis venom system. (A) Magnetic resonance imaging of the V. komodoensis head showing the protein-secreting mandibular venom gland, with the 6 compartments colored in alternating red and pink (C1–C6), and the mucus-secreting infralabial gland in yellow (L).
(B) Longitudinal MRI section showing the large duct emerging separately from each compartment of the mandibular venom gland and threading between the mucus lobes of the infralabial gland to terminate between successive teeth (black oval areas).
(C) Transverse MRI section showing the large central lumen of the mandibular venom gland and individual lobes of the labial gland.
(D) Transverse histology of Masson’s Trichromestained section showing the intratubular lumina of the mandibular venom gland that feed into the large central lumen.
(E) Transverse histology of Masson’s Trichrome-stained section of a mucus infralabial gland showing numerous tightly packed internal lobules (note that the 6 large dark folds are histology artifacts).

The predatory ecology of Varanus komodoensis (Komodo Dragon) has been a subject of long-standing interest and considerable conjecture. Here, we investigate the roles and potential interplay between cranial mechanics, toxic bacteria, and venom. Our analyses point to the presence of a sophisticated combined-arsenal killing apparatus. We find that the lightweight skull is relatively poorly adapted to generate high bite forces but better adapted to resist high pulling loads. We reject the popular notion regarding toxic bacteria utilization. Instead, we demonstrate that the effects of deep wounds inflicted are potentiated through venom with toxic activities including anticoagulation and shock induction. Anatomical comparisons of V. komodoensis with V. (Megalania) priscus fossils suggest that the closely related extinct giant was the largest venomous animal to have ever lived.

Keywods: evolution, phylogeny, squamate, protein, toxin

Fry, B., Wroe, S., Teeuwisse, W., van Osch, M., Moreno, K., Ingle, J., McHenry, C., Ferrara, T., Clausen, P., Scheib, H., Winter, K., Greisman, L., Roelants, K., van der Weerd, L., Clemente, C., Giannakis, E., Hodgson, W., Luz, S., Martelli, P., Krishnasamy, K., Kochva, E., Kwok, H., Scanlon, D., Karas, J., Citron, D., Goldstein, E., Mcnaughtan, J., & Norman, J. 2009. A Central Role for Venom in Predation by Varanus komodoensis (Komodo Dragon) and the Extinct Giant Varanus (Megalania) priscus. Proceedings of the National Academy of Sciences